The present invention relates to a rubber composition for a tire and a run flat tire having a reinforcing layer comprising the same.
At present, a run flat tire having a side reinforcing layer (a reinforcing layer) with high hardness arranged at the inside of a side wall part is practically used, and a vehicle can run for a certain distance even if an air pressure is lost by puncture. Thereby, there is no necessity to always have a spare tire ready, and it can be expected that a weight of the whole vehicle is light-weighted. However, there is limitation on a speed and a distance for run flat running at puncture of a run flat tire, therefore, further improvement in durability of the run flat tire is desired.
As effective means for improving durability of the run flat tire, an example is a method of suppressing deformation by thickening a reinforcing layer and preventing fracture by the deformation. However, since the tire weight is increased, it opposes to the weight decrease which is the initial purpose of the run flat tire.
Further, there is also a method of increasing an amount of a filler for reinforcement such as carbon black and enhancing the hardness of a reinforcing rubber to suppress deformation. However, since load to a kneader in the steps of kneading, extrusion and the like is large, and heat generation in physical properties after vulcanization becomes large, the improvement in durability of the run flat tire cannot be largely expected.
Further, as effective means for improving durability of the run flat tire, an example is a method of increasing a vulcanization density by using a large amount of a vulcanizer and a vulcanization accelerator without increasing an amount of carbon black and suppressing deformation and heat generation (for example, the JP-A-2002-155169). However, elongation of a rubber is lessened, and strength at break is lowered.